Field of the Invention
The present invention relates to a manufacturing method and an injection molding system for a multi-color molded article.
Description of the Related Art
In general, multi-color molded articles are assumed to be products that are obtained by simultaneously or sequentially injection-molding resins of a plurality of types or colors. In this specification, however, all those molded articles which are obtained by simultaneously or sequentially injection-molding even resins of the same type or color by means of a plurality of injection units are referred to as multi-color molded articles. Further, the multi-color molding described herein is a method of simultaneously or sequentially injection-molding resins by means of a plurality of injection units.
There are two known methods of manufacturing multi-color molded articles as follows:
(1) a method using a multi-color molding machine; and
(2) a method based on molded article transfer between a plurality of injection molding machines.
Further, the method (1) includes:
(1A) a submethod in which resins of a plurality of types are simultaneously injected into one mold using a single injection molding machine comprising a plurality of injection units; and
(2A) a submethod in which resins of a plurality of types are sequentially injection-molded with molds alternately exchanged by means of a single injection molding machine comprising a plurality of injection units and a mechanism for rotating the molds.
In the method (2), on the other hand, processes are repeated such that a primary molded article injection-molded by a first injection molding machine is set in a predetermined position of a mold of a subsequent or second injection molding machine and injection-molded by the second injection molding machine, and that the resulting molded article is further set in a mold of another subsequent or third injection molding machine and injection-molded.
Japanese Patent Application Laid-Open No. 2009-73151 discloses a manufacturing method for a two-color molded article in which a primary molded article is set in a second injection molding machine by an industrial robot.
Further, Japanese Patent Application Laid-Open No. 4-265719 discloses an insert injection molding method using a single injection molding machine. According to this method, injection molding is performed in such a manner that an insert-molded article is taken out along with an insert mold from a mold and recovered, a new insert is attached to an insert mold, and the insert mold fitted with the new insert is mounted in a mold of an injection molding machine. This conventional method for insert injection molding using the single injection molding machine is different from a manufacturing method for a multi-color molded article according to the present invention in which a plurality of injection molding machines are used for multi-color molding.
The method (1) has a problem that the injection molding machine and mold are usually custom-made, so that they are costly and not versatile. According to the method (2), in contrast, the problem of high cost and lack of versatility of the injection molding machine and mold can be solved. Since the transferred molded article is not in close contact with the destination mold surface, however, resins of second and subsequent colors may penetrate between the molded article and the mold surface, possibly resulting in an undesired product. This problem is particularly acute for optical elements, exterior parts, and other products whose surface shapes are critical.